This invention relates to methods and apparatus for image processing and more particularly to image enhancement. In particular, the invention relates to methods and apparatus for the enhancement of both video images of natural scenes that contain a wide range of spatial frequencies and of real-world views of natural scenes.
Traditional image enhancement methods suffer from a number of drawbacks. Many traditional image enhancement methods can not effectively enhance images over a wide band of spatial frequencies. For example, one technique enhances an image by changing its spatial frequency content through manipulation of the coefficients of a discrete cosine transform (“DCT”) of the image. The method segments the image into 8×8 pixel sections and obtains the cosine transform of each section. This technique fails to capture low frequency components that arise as a result of features that have significant variations in luminance mainly over an area larger than an 8×8 pixel section. Other techniques process an image in the spatial domain. Such techniques typically enhance the image only over a narrow range of frequencies. See E. Peli, “Limitations Of Image Enhancement For The Visually Impaired,” Optometry and Vision Science, vol. 6, pp. 15-24 (1992); and E. Peli, E. Lee, C. L. Trempe, S. Buzney, “Image Enhancement For The Visually Impaired: The Effects Of Enhancement On Face Recognition”, Journal of Optical Society of America, vol. 11 pp. 1929-1939 (1994).
Therefore, such traditional image enhancement techniques are not suitable for enhancing the images of many natural scenes that contain a wide range of spatial frequencies. Further, human observers detect moving objects that contain a wide band of frequencies more readily than those with a narrow band of frequencies. Thus, the traditional techniques are not appropriate in systems for assisting detection of moving objects, or in systems that provide real-time viewing enhancement of natural scenes.
Traditional methods also can not readily enhance an image while the size of the image changes. For example, the viewer of a digital television display could desire to follow the image of an object that undergoes a large change in its size while maintaining a selected degree of enhancement. The ability to enhance a wide range of frequencies is crucial in such applications. Traditional techniques, such as a DCT method or other band-limited methods are not appropriate for such applications because they provide a limited range of spatial frequencies of the image.
In addition, traditional enhancement methods, both in the spatial domain and in the frequency domain, typically manipulate a large fraction of pixels. As a result, their use in the enhancement of color pictures requires tracking the color content of many pixels while the computation changes the luminance of those pixels.
Accordingly, it is an object of this invention to provide methods and apparatus for enhancing images over a wide band of spatial frequencies.
It is another object of the invention to provide methods and apparatus that can readily enhance such images over a reasonable range of image sizes.
It is yet another object of the invention to provide methods and apparatus for real-time viewing enhancement of natural scenes.
It is a further object of the invention to provide methods and apparatus for better enhancement of color pictures.
It is yet a further object of the invention to provide methods and apparatus for expanding field of view of a patient suffering from peripheral field loss.
The invention is next described in connection with illustrated embodiments. It will, however, be obvious to those skilled in the art that various modifications can be made in the embodiments without departing from the spirit or scope of this invention.